Forging is one of the oldest molding methods to change shapes by putting outside force into metals. Since ancient times, people have been making tools, arms, and other instruments they need by heating and beating metals using hammer & Anvil. Today's forging is one of the far-reaching metal processing methods, and it can be said to be the ancient art which exists till now. Forging products came to ensure their position in the industry through new & more improved forging method and the improvement of the equipments according to the discovery of new metal & development of alloy. Especially, owing to the development of motors, forging industry came to develop rapidly with the age lighter metal products having superior mechanical property have to be supplied cheaply. Still free forging hammer exists as one of the industrious machine, however, high-efficient forging machines are being developed and used. In addition, automation is spreading to the various fields of forging industry because it can lower cost through reduction of labor force & manufacturing expenses. Every forging process begins from the preparation of materials including inspection, cutting & heating of materials. Generally, preliminary forging is Rough-Shaping step.(in many cases, goods are produced without preliminary forging.) Next is Die Forging, and then, Trimming works. Finally, there’s post processing including testing, inspection, heat treatment, surface treatment.
The aim of forging is tempering & molding.
Tempering means a work to improve structure through pressing pore, segregation, pipe & excessive structure as the internal defects of steel ingot and minimizing crystals. And molding is to make certain kinds of shapes from steel ingot. Therefore, forging aims to improve the mechanical property of slag through tempering and reduce post processing or processing numbers through making shapes by molding.
Forging can be classified diversely according to existence or nonexistence of mold, temperature of materials and forging machines. Here, let's inspect meaning of several kinds used generally.
Free forging means molding without using the specific mold and it is different from Die forging. Free forging spends less energy to be required for molding than Die forging because it has no constrain by a mold. Therefore, it's suitable for large forging products which can't use a mold, and it's also suitable for small products having small quantity because it doesn't need any special mold. However, there are demerits like slow working speed, non accurate measurement, and much time & costs for cutting process during post processing compared with Die forging.
Die forging is a method to mold using the specific mold and is different from Free forging. Because Die forging requires much energy to transform the materials, generally, it's molded at the high temperature having the least transformation resistance of the materials, and it's called Hot Forging. On the other hand, it's called Cold Forging to mold at the normal temperature. Die forging can obtain the superior tempering effects because of retempering to use rolling steel materials, and it can produce much forging products with the same mold. Therefore, it can reduce cutting time & expenses because it can obtain the forging products having superior precision. However, forging equipments of Die forging is high-price compared with Free forging, and it's not suitable for production of small quantity because it has to produce the required mold. It has the advantage in mass production of motor parts or farm machine parts.
As a method to heat materials more than recrystal temperature, though it's short for precision compared with Warm & Cold Forging, it's generally used because of lower production expenses & little restriction to the shape of forging products.
As a method to perform at the medium temperature between Hot & Cold Forging, it has better precision than Hot Forging but worse than Cold Forging.
As a method to perform at the normal temperature or near without heating the materials, it can obtain the best forging products in respects of precision. However, the materials for forging are limited to middle? low carbon steel or low alloy steel because of much transformation resistance at the normal temperature. And it has the demerits that shapes are restricted to axially symmetrical.
Several blows have to be done to obtain necessary shapes in Hammer forging. In case of general Die forging, blows more than one are performed by each process For example, in case of Connecting Rod, firstly, drawing works for I-Beam part are performed, and processes of Blocker& Finisher, and then Trimming at the machine prepared specially. The productivity & quality of forging products in this Hammer Forging depend on the skills of Hammer Operator.
Press forging is performed through working of one times by each process. Also, Press forging has the narrow range to work the preliminary molding (Rough-Shaping ) compared with Hammer Forging. Therefore, in case Rough-Shaping is required, there are many cases to use the special equipments. For example, in case of Connecting Rod, it's the general method of Rough-Shaping at the special Forging Roll Machine and perform only Blocker & Finisher at the Forging Press because the drawing work of I-Beam part isn't smooth compared with Hammer forging. (In case, Trimming can be performed at forging press.) However, Press Forging has the merit that the unskilled can operate because the ratio of depending on the operator's skill is lower compared with Hammer forging.
Upsetter is the forging machine composed of Grip Die opened & closed up and down or right and left, and Punch (Heading Tool) to move back and forth. Upsetter is mostly used for forging with Flange at the end of long spindle. And it's used for the products having Flange at the middle, having a penetrated hole and a big hole unpenetrated in addition to forging of pipe. The representative forging product by Upsetter is Rear Axle Shaft for motors. And Drive Pinion, Hub Casing, Drag Link, Stem are also produced from Upsetter. Furthermore, Upsetter Forging is being used to produce preliminary Rough-Shaping for Hammer or Press Forgings.
Roll forging is the method to draw to the length direction while decreasing cross section area through passing Round Bar or Square bar to the directions of rotation & right angle of Roll between a pair of Roll rotating to the opposite direction. Generally, Roll mold has one or several Grooves. Roll forging is mostly used for long products like Front Axle of motors and for volume distribution of the preliminary forging products(Rough-Shaping) for forging ones having many volume changes of each cross section to the length direction including Connecting Rod. In addition, it's used for drawing spindle parts of Rear Axle Shaft.
As a forging machine composed of Main Roll, Mandrel and one Axle Roll of each up & down, it's work to make necessary shapes through increasing the diameter by pressing Rough-shaping of Ring shape. Working process is firstly to cut the materials, heat with Upsetting at Hammer or Press, produce Rough-Shaping through Punching the inside diameter, and then increase the diameter according to the necessary shape at the Ring Rolling machine. In addition, there are various forging methods including Cross Rolling, Powder Forging, Squeeze Forging and Shake forging.
After manufacturing the top part to the height of 0.3mm at the Press step, the final height comes to be 0.1mm through 0.2mm cutting at the working of Hair line.